1. Field of the Invention
This invention relates generally to the projection of visible lines onto surfaces upon which persons may be standing (e.g., athletic fields during sporting or entertainment events) and, more particularly, to systems employing laser light beam sources to generate such visible lines.
2. Discussion of the Background Art
In the game of football, a key objective of the team in possession of the ball (i.e., the “offense”) is to retain possession of that ball by moving it far enough down the field. Specifically, the offense is given a set of four plays or “downs” to advance the ball by at least ten yards. Each time that distance is reached or exceeded, the offense is said to have crossed a “first down” line, a new set of downs is earned, and the offense is allowed to continue its advance toward the goal line of the opposing team (i.e., the “defense”). If the offense falls short, however, possession is lost and the two teams reverse their roles. A regulation football field has a length of 100 yards and 53 yards. Thus, by way of example, a team gaining possession of the ball at its own 20 yard line must move the ball a total of eighty yards in order to reach the end zone of the opposing team.
In numerous occasions throughout an average football game, the officials of the game must resort to sideline markers to establish whether the offense has advanced the ball by the required distance. The standard alignment system that is utilized is generally a pair of poles connected by a 30 foot long chain. The relative position of the football is measured by locating a first of these poles at the approximate location of the initial line of scrimmage and moving the second as far forward as possible. Each time this measurement is made, the game must be delayed and the yard markers must be carried from the sidelines to the place on the field where the official has “spotted” the ball. Although the game of football has become a relatively complex sport, involving literally hundreds of millions of invested dollars, this time consuming system has remained relatively the same since the conception of the sport.
A number of approaches intended to ameliorate the aforementioned deficiencies have been proposed over the years, but none of them has met with any degree of commercial success. U.S. Pat. No. 3,741,662, entitled “VISIBLE LINE MARKER” and issued to Pioch on Jun. 26, 1973, U.S. Pat. No. 3,752,588, entitled “LASER FOOTBALL FIRST DOWN MEASURING DEVICE” and issued to Chapman on Aug. 14, 1973, and U.S. Pat. No. 4,090,708 entitled “APPARATUS FOR MARKING FOOTBALL FIELDS” and issued to McPeak on May 23, 1978. Each of the aforementioned patents involve the use of lasers for the purpose of marking visible lines of demarcation on an athletic field. One of the principal drawbacks of these systems is the time-consuming and tedious method of operation.
Both Chapman and Pioch involve the use of track mounted, sliding projectors that are located at the sidelines and several feet above the field level. The lasers are mounted for oscillation in a vertical plane and the projected, low intensity beam developed by each must strike the field at points of reference lying on an imaginary line of demarcation defined by the intersection of the vertical plane with the field surface. Accordingly, it is necessary for the operator to manually position the projector for each reference point established. Like Pioch and Chapman, McPeak discloses the use of a laser assemblies adapted to accommodate sliding movement along the sidelines of a football field. McPeak, however, teaches that two oppositely directed beams should be aimed at a level above (i.e., “adjacent and parallel to”) the field surface.
Another drawback associated with the aforementioned systems is that the low-intensity output of these lasers is far too low to be visible by the players, let alone by an audience in, for example, a stadium setting. Indeed, the aforementioned systems are intended for use only in making a first down measurement determination after each close play. As it turns out, players intent on getting the ball past the first yard line—and focused on the sideline markers long enough to be “blindsided” by the defense—have suffered very serious neck and back injuries.
Television networks have recently implemented an image pre-processing system which allows viewers of televised football games to see a so-called “virtual” first down line that digitally projects, in real time, a visible line onto video frames recorded by the television camera, the line being displayed on a viewer's television set so that it appears to extend between the first down sideline markers. Unfortunately, neither the players, game officials, nor the fans attending such games can actually see this virtual line. It is thus reasonable to conclude that given the rapid and widespread adoption of a virtual visible line marking system—whose enjoyment is strictly limited to television viewers, it has heretofore been deemed impossible or impracticable to project a real, visible line onto the grassy surfaces which characterize most athletic fields.
A continuing need therefore exists for a visible line or image marking system that is simple to operate, accurate enough to allow its use by officials at sporting events, and of sufficient intensity to be viewed by players, large audiences, and television viewers alike.
A need also exists for a system capable of projecting, onto surfaces that are characterized by uniform and/or non-uniform topological features, a line which can be seen from different perspectives and from considerable distances—even in daylight conditions.
A need also exists for a system that is capable of projecting a line which, though intense enough to be seen from a wide range of viewing angles, conforms to all applicable eye-safety regulations such as those promulgated by the FDA's Center for Diagnostic and Radiological Health (CDRH).
A need also exists for a system that is flexible enough so that it can be used to project images comprising one or more linear or curvilinear line segments, with the images being either monochromatic or multicolored, as desired.